1. Field of the Invention
The present invention relates to an oil-based foam drilling fluid for oil and/or gas wells and for methods of making and using same.
More particularly, the present invention relates to an oil-based foam drilling fluid (OBFDF) for oil and/or gas wells, where the composition includes a base oil, a foaming agent, and a hydrocarbon soluble polymer comprising a polymer of a styrene monomer and a diene monomer. The foam is stable at a temperature of at least 350° F. The present invention also relates to methods of making and using same.
2. Description of the Related Art
Recently, an oil-based foam drilling fluid (OBFDF) was developed and described in U.S. patent application Ser. No. 11/293,859 filed Dec. 2, 2005, published as US 2007/0129257 and issued as U.S. Pat. No. 7,797,928 on 08/03110. However, the use of this OBFDF fluid for underbalanced and near balance drilling applications is limited by undesirable foam stability (half life time) and undesirable temperature stability, when two organophillic phases (e.g., oil and nitrogen) are employed. When the continuous phase is crude oil, diesel, mineral oil, alpha olefins and/or ester based oils and the foam gas is nitrogen, then the generation of foams that are stable at high temperatures is difficult and has not been achieved to our knowledge.
Generally, to create a stable foam in such environments, foaming systems including mainly fluoro surfactants and/or silicon based surfactants are used.
Alternatively and historically, the problem of generating a stable, high temperature foam in fluids including two organophilic phases has been solved either by changing the gas phase to carbon dioxide or slightly viscosifying the liquid phase with ortho phosphate ester systems using Al or Fe cross-linking agents or with other types of polymers. This alternative requires delicate balance in the amounts of the phosphate ester and cross linking agent, which is difficult to manage by those skilled in the art.
Thus, there is a need in the art for an oil-based foam drilling fluid that does not suffer from the deficiencies of prior art oil-based foaming systems and produces stable foams in fluids including two organophilic phases that are stable even in high temperature environments.